The manufacture and various uses of polyolefin-based fibers and corresponding nonwoven materials are well known in the textile art. Attempts to apply such knowledge to produce products in the area of personal hygiene, such as cover stocks for catamenial devices, disposable diapers, and incontinence pads, have met with limited success. Such products must have a fluid-absorbent core, usually comprising one or more layers of fluid absorbent material such as wood pulp, gauze, or tissue and, in some cases, synthetic hydrophilic material, such as hydrophilic polyurethane foam.
The fluid-absorbing material is typically provided in the form of a thermally bonded pad. To protect the clothing or areas around the user from being stained or wetted by fluids absorbed by the pad, the pad may be backed by a fluid impervious barrier sheet. The absorbent product is typically positioned against the body with the hydrophilic material facing and contacting the body and the fluid impervious barrier layer facing the outside. To enhance a sense of comfort, such absorbent products also generally employ a facing or cover stock material which covers the body-facing surface of the product. The facing or cover stock must be very pervious to fluids on the side of the product that is placed against the body, and yet be essentially nonabsorbent. Such material should also feel smooth and soft to the touch. In addition, certain additional characteristics are also sometimes desired, such as visual opacity, specific coloring, and luster on the outer surfaces.
In order to obtain many of above-listed characteristics, a cover stock utilizing essentially hydrophobic polymeric material, such as polyolefin fiber or film, may be made at least temporarily hydrophilic yet have the continuing ability to pass aqueous fluids through. This is particularly important in the case of diaper cover stock so as to avoid lateral liquid migration and side leakage without interfering with fabric bonding steps or wet strength of the final product.
Based on the teaching in the paper-making art, it is known that short term hydrophilicity can be imparted to hydrophobic polymers such as polyolefin fiber by using flash evaporation techniques and treating the resulting fiber or filament with hydrophilizing agents such as polyvinyl alcohol or various nitrogen-containing water-soluble polymers. U.S. Pat. Nos. 4,156,628, 4,035,229, 4,082,730, 4,154,647, 4,156,628, 4,273,892 and 4,578,414 are indicative of this teaching. Efforts to incorporate an alkoxylated alkylphenols or corresponding polyoxyalkylenes into spun melt fiber compositions is disclosed in U.S. Pat. No. 4,578,414.
U.S. Pat. No. 5,033,172 discloses that the hydrophilicity and liquid strike through properties of fiber (both continuous and staple), fibrillated film and corresponding nonwoven materials can be obtained and retained for an extended period by incorporating into the corresponding polyolefin-containing cast or spin melt composition, and an effective amount of a modifier composition. The modifier composition may compromise (a) at least one N,N-polyalkoxylated 10-22 carbon fatty acid amine, inclusive of amines having 12-20 carbon and preferably 18 carbon linear straight chain moiety such as octadecyl amine or octadecenyl amine; and (b) up to about 60%, and preferably 0-45% by weight of modifier composition, of a primary or secondary 10-22 carbon fatty acid amide such as stearamide. After spinning or casting the resulting melt to obtain fiber or film, then processing the fiber or film in accordance with the techniques disclosed in U.S. Pat. Nos. 4,310,594 and 3,576,931, the corresponding webs can be oriented and bonded by conventional means to obtain the desired non-woven material. Such treated fiber can, if desired, be a continuous or staple bicomponent fiber such as a sheath/core variety in which the polyolefin sheath spun melt contains the modifier composition of the homogeneous (e.g. monoolefin) type.
In U.S. Pat. No. 4,853,290, issued to Apostol Yanidis on Aug. 1, 1989, a blend of ethylene-acrylic acid copolymer and ethylene-methylacrylate copolymer is coextruded onto a polypropylene film to serve as an adhesive or tie layer to a second polymer applied to it.
In U.S. Pat. No. 4,782,110, issued to James R. Wolfe, Jr. on Nov. 1, 1988, melt processible multi-phase thermoplastic compositions are described which can be formed into various shapes by compression molding, injection molding, blow molding and extrusion, and said to be useful for automotive parts, e.g. automotive boots, seals, gaskets, tubing, reinforced hose, film and sheeting. The composition comprises a blend of (a) 15-75 parts by weight of a crystalline polyolefin resin forming the continuous phase of the composition, and (b) 25-85 parts by weight of a crosslinked elastomer of an ethylene alkyl acrylate copolymer consisting essentially of units derived from ethylene, an alkyl ester of acrylic acid wherein the alkyl group contains 1-6 carbon atoms, and a monoalkyl ester of 1,4-butenedioic acid wherein the alkyl group contains 1-6 carbon atoms, forming the discontinuous phase of the composition.
U.S. Pat. Nos. 3,373,222 and 3,373,223 each issued on Mar. 12, 1968 to Robert G. Armstrong disclose polymeric blends comprising polyolefin resin, polyamide resin, and either a carboxylated polyethylene, an ethylene-acrylic or a methacrylic acid copolymer. Homogeneous polymeric blends have utility in the preparation of films useful in the packaging industry, and in the preparation of plastic bottles and other containers which require a high degree of impermeability.
U.S. Pat. No. 5,033,172 discloses a hydrophobic polyolefin containing nonwoven material which may contain up to 60% by weight a particular modifier composition. U.S. Pat. Nos. 4,540,414 and 4,550,725 disclose a nonwoven polypropylene fabric designed for removal of moisture from the skin of human beings covered by the fabric. U.S. Pat. No. 4,892,532 discloses a particular arrangement of liquid absorbing fabrics and fabric layers suitable for forming a diaper material. U.S. Pat. No. 4,804,378 discloses a material suitable for forming a sheet having a hydrophilic surface and a hydrophobic inside.
U.S. Pat. No. 4,304,234 discloses bonded polyolefin filaments for forming nonwoven fabrics, and a process for spinning nonwoven fabrics. U.S. Pat. No. 3,509,009 provides an early teaching of nonwoven fabrics. U.S. Pat. No. 4,734,445 discloses a latex composition suitable for applications requiting surface hydrophilicity, including various nonwoven fabrics and paper products. U.S. Pat. No. 4,372,310 discloses woven panels for diapers, and U.S. Pat. No. 4,892,534 discloses nonwoven webbed materials for diapers, incontinent products, and feminine care napkins. U.S. Pat. No. 4,372,312 discloses a nonwoven hydrophilic web suitable for a pad material, and U.S. Pat. No. 4,868,031 discloses various polyolefin fiber-containing nonwoven materials. European Patent Publication Nos. 0307116 and 0192965 disclose both porous films and absorbent layers for various sanitary articles.